Regeneration method of silicon-aluminum molecular sieve and catalyst for preparing aromatic hydrocarbon through CO2 hydrogenation by using silicon-aluminum molecular sieve

Abstract

The invention discloses a regeneration method of a silicon-aluminum molecular sieve, which is characterized by comprising the following steps: dissolving carbon deposition of an inactivated silicon-aluminum molecular sieve in a supercritical carbon dioxide fluid, pickling, and synthesizing a regenerated silicon-aluminum molecular sieve by using the dissolved carbon deposition as a silicon source and an aluminum source. The method overcomes the problems of low efficiency, large structural damage, high cost and pollution of a traditional regeneration technology, efficiently removes carbon deposition and recovers a molecular sieve pore structure and an acidic active center through multi-step synergy, is high in regeneration efficiency, environment-friendly, pollution-free and low in cost, remarkably improves the conversion rate of carbon dioxide and the selectivity of aromatic hydrocarbon in the reaction of preparing aromatic hydrocarbon through hydrogenation of carbon dioxide, and has a wide application prospect. Good industrial application prospects are realized.

Description

Technical Field

[0001] The present application relates to a regeneration method of a silicon-aluminum molecular sieve and a CO2 hydrogenation catalyst for producing aromatics using the same, and specifically to the co-regeneration of a ZSM-5 molecular sieve using supercritical CO2, belonging to the field of chemical industry. Background Art

[0002] Aromatic hydrocarbons, as important basic chemical raw materials, are widely used in plastics, rubber, fiber, pharmaceuticals, fragrances, and other fields. Traditional aromatic hydrocarbon production relies heavily on fossil resources, which not only faces resource shortages but also results in significant carbon emissions. Therefore, the direct synthesis of aromatic hydrocarbons through carbon dioxide hydrogenation has both economic and environmental significance.

[0003] In the reaction system of carbon dioxide hydrogenation to aromatics, the molecular sieve ZSM-5, due to its unique pore structure, has a shape-selective catalytic effect on the reacting molecules, which can promote the formation of aromatic products and inhibit the occurrence of side reactions. However, during the reaction process, carbon deposition is one of the main causes of its deactivation. Carbon deposition not only blocks the pores of the molecular sieve, hindering the diffusion and mass transfer of reactants and products, but also covers the acidic active centers on the surface of the molecular sieve, changing its acid distribution and strength, thereby significantly reducing the catalytic activity and selectivity of the molecular sieve.

[0004] In addition, a large amount of water is generated in the reaction of hydrogenating carbon dioxide to produce aromatics. Under the high temperature and high pressure reaction environment, the ZSM-5 zeolite is easily affected by hydrothermal effects and undergoes structural damage. It may also change its acid distribution and strength, thereby affecting the catalytic activity and selectivity of the zeolite.

[0005] Currently, the main methods for regenerating deactivated ZSM-5 molecular sieves include traditional methods such as thermal regeneration and solvent extraction regeneration. Patent CN109759148B proposes that the traditional thermal regeneration method can be improved by exchanging gases and temperatures in multiple steps. This method can effectively remove carbon deposits covering active sites and carbon deposits in micropores, restore acid sites, and thus expose active centers within the catalyst micropores, further improving the regeneration level of the catalyst. However, this method requires replacing the reactor and is complex to operate, and no data on the catalyst activity after regeneration is provided. The solvent extraction regeneration method uses a suitable organic solvent to treat the deactivated ZSM-5 molecular sieve, removing carbon deposits and other impurities in and on the molecular sieve pores by dissolution or extraction. This method has mild operating conditions and minimal damage to the molecular sieve structure, but the extraction efficiency is relatively low. It is difficult to completely remove impurities that are deeply deposited or tightly bound to the molecular sieve. In addition, the recovery and treatment of the organic solvent is relatively complex and costly, which cannot meet industrial needs. Patent CN109759148B believes that the molecular sieve crystallization regeneration method does not require grinding of the waste molecular sieve, removing carbon deposits or impurities. Instead, the waste molecular sieve is directly used as a silicon and aluminum source, and a template and seed crystals are added to crystallize in a reactor to obtain a regenerated molecular sieve. The original silicon and aluminum elements of the waste molecular sieve are directly crystallized and regenerated under conditions of extremely low water consumption. Compared with fresh commercial molecular sieves, the reaction activity and life indicators are close. However, if the molecular sieve is severely carbon-deposited and no carbon removal treatment is performed, it is difficult to remove the carbon deposits in the molecular sieve micropores and release active sites by simply synthesizing the molecular sieve again.

[0006] Therefore, developing a regeneration method that is simple to operate, economical, and can effectively restore the catalytic performance of ZSM-5 zeolite is crucial for maintaining the long-term stable operation of the carbon dioxide hydrogenation to aromatics reaction and improving the economy and competitiveness of the process. Summary of the Invention

[0007] The purpose of the present invention is to provide a ZSM-5 molecular sieve regeneration method for producing aromatics by hydrogenating carbon dioxide, which utilizes supercritical fluid, ultrasonic acid washing and molecular sieve resynthesis to solve the problems of eliminating carbon deposits, waste molecular sieve treatment and production costs, and promote the industrial application of carbon dioxide hydrogenation to produce aromatics technology.

[0008] According to one aspect of the present application, a method for regenerating a silicon-aluminum molecular sieve is provided, characterized in that the carbon deposits of the deactivated silicon-aluminum molecular sieve are dissolved with supercritical carbon dioxide fluid, and then acid-washed to use the silicon and aluminum sources to synthesize the regenerated silicon-aluminum molecular sieve.

[0009] Specifically, the regeneration method of the silicon-aluminum molecular sieve comprises the following steps:

[0010] a) Pretreatment

[0011] placing the deactivated silica-alumina molecular sieve in an inert atmosphere and pretreating it at 120-300° C. for not less than 1 hour to obtain a pretreated sample;

[0012] b) Supercritical carbon dioxide fluid treatment

[0013] placing the pretreated sample in a supercritical fluid reaction device to perform supercritical carbon dioxide fluid treatment to obtain a supercritical carbon dioxide fluid-treated sample;

[0014] c) Ultrasonic pickling

[0015] placing the sample treated with supercritical carbon dioxide fluid in an acidic solution and performing acid washing in ultrasound to obtain an ultrasonically acid washed sample;

[0016] b) synthesizing the regenerated silica-alumina molecular sieve

[0017] The ultrasonically acid-washed sample is used as a silicon source and an aluminum source to synthesize the regenerated silica-alumina molecular sieve.

[0018] Preferably, the inert atmosphere in step a) is selected from one or more of N2, Ar or He.

[0019] Step a) is used to remove carbon deposits and moisture adsorbed on the catalyst surface.

[0020] Preferably, the conditions for the supercritical carbon dioxide fluid treatment in step b) are: temperature of 30-40° C., pressure of 7-9 MPa, and treatment time of 2-3 h.

[0021] Preferably, the step b) comprises placing the pretreated sample in a supercritical fluid reaction device, performing supercritical carbon dioxide fluid treatment, and then reducing the pressure to normal pressure to obtain a supercritical carbon dioxide fluid treated sample.

[0022] Preferably, the pressure reduction rate to normal pressure is 0.5-1 MPa / min.

[0023] In the supercritical carbon dioxide fluid treatment step, supercritical CO2 has both high gas diffusivity and strong liquid solubility, and is used to dissolve carbon deposits in the molecular sieve pores.

[0024] Preferably, the acidic solution in step c) is a dilute nitric acid solution with a mass fraction of 5-10%; and the pickling time is 30-60 minutes.

[0025] In the ultrasonic pickling step, ultrasonic oscillation and mechanical stirring are used to enhance the reaction between dilute nitric acid and residual carbon deposits and adjust the acid sites of the molecular sieve. Dilute nitric acid can also be replaced by other inorganic acids.

[0026] Preferably, step d) is: adding alkali, organic template, and silica sol to the sample after ultrasonic acid washing, and then performing hydrothermal crystallization to obtain the regenerated silica-alumina molecular sieve.

[0027] Specifically, the silica-alumina molecular sieve is a ZSM-5 molecular sieve; step d) comprises: the silicon source and the aluminum source include pseudo-boehmite, a binder added during molding, and the amount of silica sol added is calculated based on the aluminum content in the binder, so that the final silicon-aluminum molar ratio is 100 to 200. Further preferably, the sample after ultrasonic pickling is used as the silicon source and the aluminum source, a sodium hydroxide solution with a mass fraction of 1% to 4% and a template agent tetrapropylammonium hydroxide are added and stirred for 30 minutes, and the silica sol is added dropwise, and the mixture is stirred at 80°C for 2 hours, stirred at room temperature for 20 hours, and crystallized at 180°C for 48 hours to obtain the regenerated ZSM-5 molecular sieve.

[0028] According to another aspect of the present application, a catalyst for producing aromatics by hydrogenating CO2 is provided, wherein the catalyst is a composite catalyst composed of a regenerated ZSM-5 molecular sieve obtained by the regeneration method, which is washed, dried and calcined, and an iron-based catalyst.

[0029] The drying condition is 80-120° C. for 12 hours.

[0030] The calcination condition is 500-600° C. for 3-6 hours.

[0031] Optionally, the composite catalyst is obtained by washing, drying, calcining, tableting, and crushing regenerated ZSM-5 molecular sieve into 20-40 mesh sizes, and then mechanically mixing with a 20-40 mesh iron-based catalyst.

[0032] Optionally, the composite catalyst is obtained by mechanically mixing a powder sample of a regenerated ZSM-5 molecular sieve that is washed, dried, and calcined with a powder sample of an iron-based catalyst, followed by tableting and crushing into 20-40 mesh sizes.

[0033] Optionally, the composite catalyst is a bed catalyst, the upper layer is filled with Fe-based catalyst particles of 20 to 40 mesh, and the lower layer is filled with regenerated ZSM-5 molecular sieve that has been washed, dried, calcined, pressed into tablets, and crushed into 20 to 40 mesh. The two layers are in direct contact or separated by inert materials such as quartz sand or quartz wool (thickness 1 to 2 cm).

[0034] According to another aspect of the present application, a method for producing aromatics by hydrogenating CO2 is provided, which uses the above-mentioned catalyst for producing aromatics by hydrogenating CO2;

[0035] The reaction pressure is 2-3 MPa, the reaction temperature is 280-340° C., and the space velocity is 2000-20000 mL / (g·h).

[0036] The beneficial effects of this application include but are not limited to:

[0037] (1) High regeneration efficiency: Through the synergistic effect of a series of steps, including supercritical fluid treatment, ultrasonic-assisted acid cleaning, regeneration and synthesis of spent molecular sieves, and drying and calcination, the carbon deposits on the surface and in the pores of the deactivated ZSM-5 molecular sieve can be efficiently removed, and the pore structure and acidic active centers of the molecular sieve can be effectively restored, thereby significantly improving the catalytic activity of the molecular sieve. Compared with traditional regeneration methods, the regeneration method of the present invention can achieve a higher degree of activity recovery in a shorter time.

[0038] (2) Little damage to the molecular sieve structure: The supercritical fluid treatment process conditions are mild and have almost no damage to the crystal structure of the molecular sieve; the ultrasonic-assisted pickling and waste molecular sieve regeneration synthesis treatment conditions can remove impurities and adjust acid sites, maintain the original structure of the molecular sieve, and extend the service life of the molecular sieve. DETAILED DESCRIPTION

[0039] The present application is described in detail below with reference to embodiments, but the present application is not limited to these embodiments.

[0040] Unless otherwise specified, all raw materials and reagents used in this application were purchased from commercial sources and used directly without treatment. The instruments and equipment used adopted the protocols and parameters recommended by the manufacturers.

[0041] As a specific embodiment, the ZSM-5 molecular sieve regeneration method for producing aromatics by hydrogenation of carbon dioxide comprises the following steps:

[0042] Pretreatment step: Place the deactivated ZSM-5 molecular sieve in an inert gas (one or more of N2, Ar and He) environment and pretreat at 120-300°C for 1-2 hours to remove small molecular impurities and moisture adsorbed on the surface of the molecular sieve.

[0043] Supercritical fluid treatment: Using supercritical carbon dioxide as a medium, the pretreated deactivated ZSM-5 molecular sieve is placed in a supercritical fluid reactor. The temperature in the reactor is controlled at 30-40°C, the pressure at 7-9 MPa, and the treatment time is 2-3 hours. Under the action of supercritical carbon dioxide, impurities such as carbon deposits are dissolved in the supercritical fluid phase. The pressure is then slowly reduced (at a rate of 0.5-1 MPa / min) to atmospheric pressure, separating the carbon deposits from the molecular sieve pores, thereby removing most of the carbon deposits.

[0044] Ultrasonic pickling: The supercritical fluid-treated molecular sieve is placed in a 5-10% by mass dilute nitric acid solution and pickled using ultrasound for 30-60 minutes. Ultrasonic vibrations promote the reaction between the dilute nitric acid and residual carbon deposits on the molecular sieve surface, further removing the deposits and optimizing the acidic sites on the molecular sieve. The product is then rinsed with deionized water and dried for later use.

[0045] The molecular sieve re-synthesis steps are as follows: the molecular sieve after ultrasonic assisted acid washing is used as the silicon source and aluminum source for preparing a new molecular sieve (including the binder pseudo-boehmite added during molding), then a sodium hydroxide solution with a mass fraction of 1%-4% and an appropriate amount of template agent tetrapropylammonium hydroxide are added and stirred for 30 minutes, and silica sol is added dropwise (the amount of silicon supplemented is calculated based on the amount of aluminum added to the binder, and the silicon-aluminum molar ratio is 100-200) and stirred at 60-100°C for 2 hours, then cooled to room temperature and stirred for 20 hours, and then crystallized at 180°C for 48 hours.

[0046] Drying and calcination steps: The regenerated molecular sieve is washed again with deionized water until neutral, then dried at 80-120°C for 12 hours to remove moisture. The dried molecular sieve is placed in a muffle furnace and calcined at 500-600°C for 3 hours.

[0047] The above-mentioned shaped molecular sieve (20-40 mesh) and Fe-based catalyst (20-40 mesh) were compounded in a mass ratio of 1:2-2:1 and used for direct hydrogenation of carbon dioxide to aromatics. The reaction conditions were: 2-3 MPa, 280-340°C, space velocity 2000-20000 mL / (g·h), and feed gas N2 / H2 / CO2 = 4 / 24 / 72 vol%.

[0048] In the embodiment, the Fe-based catalyst is prepared using the synthesis method of patent ZL201610832357.5, and the specific method is as follows:

[0049] 15.81 g of FeCl₃·6H₂O and 6.27 g of FeCl₂·4H₂O were mixed with 80 mL of water to form an iron salt solution, to which 3.5 mL of 9.0 mol / L HCl solution was added. Approximately 180 mL of 1.5 mol / L NaOH solution was added at a constant rate at 60°C with stirring. The pH of the solution was adjusted from acidic to approximately 10 over 1.5 hours. After the addition was complete, the temperature was maintained and stirred for 1 hour before cooling to room temperature. After the reaction, the deposited product was separated by magnetic field adsorption, washed once with 400 mL of deionized water, and then dried at 60°C to obtain an Fe-based catalyst powder sample.

[0050] Example 1:

[0051] 1. Pretreatment step: Take 10g of ZSM-5 molecular sieve deactivated in the carbon dioxide hydrogenation reaction to produce aromatics, place it in a N2, 30mL / min atmosphere, and pretreat it at 200℃ for 1h.

[0052] 2. Supercritical Fluid Treatment: Place the pretreated molecular sieve in a supercritical fluid reactor with supercritical carbon dioxide as the medium. Control the temperature inside the reactor to 35°C and the pressure to 7 MPa for 2 hours. After treatment, slowly reduce the pressure to atmospheric pressure to separate the supercritical carbon dioxide from the dissolved carbon deposits.

[0053] 3. Ultrasonic pickling step: The molecular sieve treated with supercritical fluid is placed in a dilute nitric acid solution with a mass fraction of 6%, and ultrasonic-assisted pickling is used for 30 minutes.

[0054] 4. Molecular sieve regeneration synthesis steps: The molecular sieve after ultrasonic assisted acid washing is used as the silicon source and aluminum source for preparing a new molecular sieve (including the binder pseudo-boehmite added during molding), and then 50 mL of a 4% mass fraction of sodium hydroxide solution and 10 mL of a template agent tetrapropylammonium hydroxide are added and stirred for 30 minutes. 3 g of silica sol (the amount of silicon supplemented is calculated based on the amount of aluminum added to the binder) is added dropwise and stirred at 80°C for 2 hours, cooled to room temperature and stirred for 20 hours, and then crystallized at 180°C for 48 hours.

[0055] 5. Drying and calcination steps: The further synthesized molecular sieve is washed again with deionized water until neutral, and then dried at 80°C for 12 hours to remove moisture. The dried molecular sieve is placed in a muffle furnace and calcined at 550°C for 3 hours.

[0056] Composite with Fe-based catalyst and reaction evaluation:

[0057] 1. The Fe-based catalyst powder sample was ground and then crushed into 20-40 mesh tablets.

[0058] 2. Preparation of composite catalyst: Weigh 0.33 g of 20-40 mesh Fe-based catalyst and 0.67 g of 20-40 mesh ZSM-5 molecular sieve catalyst and perform mechanical particle mixing.

[0059] 3. Catalyst Reaction Evaluation Procedure: Back pressure was established in the reaction gas, and the reaction gas (N2 / H2 / CO2 = 4 / 24 / 72) was fed into the fixed-bed reactor at a space velocity of 4000 mL / g / min. The reaction was conducted at a reaction pressure of 3 MPa for 50 hours. Catalyst Evaluation: 1 g of the composite catalyst was loaded into the constant temperature section of the reaction tube and hydrogen was introduced to increase the temperature. The temperature was raised at a rate of 2°C / min to the reduction temperature of 350°C. At atmospheric pressure, the temperature was maintained at a flow rate of 30 mL / min for 8 hours. The temperature was then lowered to 320°C and maintained constant. The reaction was then continued under the above reaction conditions. The CO2 conversion and aromatics product selectivity are listed in Table 1.

[0060] Example 2:

[0061] 1. Pretreatment step: Take 10g of ZSM-5 molecular sieve deactivated in the carbon dioxide hydrogenation reaction to produce aromatics, place it in a He, 30mL / min atmosphere, and pretreat it at 120℃ for 1h.

[0062] 2. Supercritical fluid treatment step: In a supercritical fluid reaction device, use supercritical carbon dioxide as the medium, control the temperature to 40°C, the pressure to 9 MPa, and the treatment time to 3 hours. After decompression and separation, proceed to the next step.

[0063] 3. Ultrasonic pickling step: The molecular sieve treated with supercritical fluid is placed in a dilute nitric acid solution with a mass fraction of 8%, and ultrasonic-assisted pickling is used for 30 minutes.

[0064] 4. Molecular sieve regeneration synthesis steps: The molecular sieve after ultrasonic assisted acid washing is used as the silicon source and aluminum source for preparing a new molecular sieve (including the binder pseudo-boehmite added during molding), and then 50 mL of a 2% mass fraction of sodium hydroxide solution and 10 mL of a template agent tetrapropylammonium hydroxide are added and stirred for 30 minutes. 3 g of silica sol (the amount of silicon supplemented is calculated based on the amount of aluminum added to the binder) is added dropwise and stirred at 80°C for 2 hours, then the temperature is lowered and stirred for 20 hours, and then crystallized at 180°C for 48 hours.

[0065] 5. Drying and calcination steps: The further synthesized molecular sieve was washed again with deionized water until neutral, and then dried at 80°C for 12 hours to remove moisture. The dried molecular sieve was placed in a muffle furnace and calcined at 550°C for 3 hours.

[0066] The steps for compounding with the Fe-based catalyst and evaluating the reaction were the same as in Example 1, with the same catalyst loading method and evaluation conditions. The CO2 conversion and aromatics product selectivity are listed in Table 1.

[0067] Example 3:

[0068] 1. Pretreatment step: Take 10 g of deactivated molecular sieve, place it in Ar, 30 mL / min atmosphere, and pretreat it at 300°C for 1 h.

[0069] 2. Supercritical fluid treatment steps: in a supercritical fluid reaction device, the temperature is 30°C, the pressure is 8 MPa, and the treatment is carried out for 2 hours.

[0070] 3. Ultrasonic pickling step: The molecular sieve treated with supercritical fluid is placed in a dilute nitric acid solution with a mass fraction of 10%, and ultrasonic-assisted pickling is used for 30 minutes.

[0071] 4. Molecular sieve regeneration synthesis steps: The molecular sieve after ultrasonic assisted acid washing is used as the silicon source and aluminum source for preparing a new molecular sieve (including the binder pseudo-boehmite added during molding), and then 50 mL of a 3% mass fraction of sodium hydroxide solution and 10 mL of a template agent tetrapropylammonium hydroxide are added and stirred for 30 minutes. 3 g of silica sol (the amount of silicon supplemented is calculated based on the amount of aluminum added to the binder) is added dropwise and stirred at 80°C for 2 hours, then the temperature is lowered and stirred for 20 hours, and then crystallized at 180°C for 48 hours.

[0072] 5. Drying and calcination steps: The further synthesized molecular sieve is washed again with deionized water until neutral, and then dried at 80°C for 12 hours to remove moisture. The dried molecular sieve is placed in a muffle furnace and calcined at 550°C for 3 hours.

[0073] The steps for compounding with the Fe-based catalyst and evaluating the reaction were the same as in Example 1, with the same catalyst loading method and evaluation conditions. The CO2 conversion and aromatics product selectivity are listed in Table 1.

[0074] Example 4

[0075] The difference from Example 3 is that the catalyst packing method is changed. The upper layer is filled with 20-40 mesh Fe-based catalyst particles, and the lower layer is filled with 20-40 mesh ZSM-5 molecular sieve particles. The two layers are in direct contact. The CO2 conversion rate and aromatic product selectivity are listed in Table 1.

[0076] Example 5

[0077] The difference from Example 3 is that the catalyst loading method was changed. The Fe-based catalyst powder and the molecular sieve-molded catalyst were ground into powder, the two powders were mechanically mixed, and then compressed into 20-40 mesh particles. The CO2 conversion rate and aromatics product selectivity are listed in Table 1.

[0078] Comparative Example 1 (thermal regeneration method):

[0079] 10 g of deactivated ZSM-5 molecular sieve was pretreated in an inert atmosphere using the same pretreatment conditions as in Example 1. Air (30 mL / min) was introduced into the pretreated reactor, and the temperature was raised to 400°C (at a rate of 2°C / min) for calcination to remove carbon deposits. The molecular sieve regeneration synthesis steps, drying, and calcination procedures were performed using the same conditions as in Example 1.

[0080] The steps of compounding with the Fe-based catalyst and evaluating the reaction were the same as those in Example 1, the catalyst filling method was the same, and the evaluation conditions were the same.

[0081] The CO2 conversion rate and aromatic product selectivity are listed in Table 1.

[0082] Comparative Example 2 (directly resynthesized without removing carbon deposits):

[0083] 10 g of deactivated ZSM-5 molecular sieve was pretreated in an inert atmosphere in the same manner as in Example 3. The molecular sieve regeneration synthesis step and the drying and calcination steps were the same as in Example 3.

[0084] The steps of compounding with the Fe-based catalyst and evaluating the reaction were the same as those in Example 1, the catalyst filling method was the same, and the evaluation conditions were the same.

[0085] The CO2 conversion rate and aromatic product selectivity are listed in Table 1.

[0086] Table 1: Reaction performance of carbon dioxide hydrogenation to produce aromatic hydrocarbons over catalysts in Examples and Comparative Examples (results after 50 h of reaction)

[0087]

[0088] Comparison of the experimental data of Examples 1, 2, and 3 with fresh catalysts for 50 hours shows that the synergistic effect between supercritical fluid treatment, ultrasonic-assisted pickling, and regeneration of spent molecular sieves effectively removes carbon deposits within the molecular sieve pores, successfully regenerating and synthesizing a new catalyst with high activity, comparable to the performance of fresh catalysts. Comparison of the experiments in Examples 3, 4, and 5 shows that the packing method of the composite catalyst has an impact on performance, with particle mixing having superior performance. Comparative Examples 1 and 2, after similar treatment, show improved performance compared to the deactivated catalysts, as shown in Table 1, but do not reach the performance level of fresh catalysts.

[0089] The above descriptions are merely a few embodiments of the present application and do not constitute any form of limitation to the present application. Although the present application discloses the preferred embodiments as above, they are not intended to limit the present application. Any technical personnel familiar with the present profession, without departing from the scope of the technical solution of the present application, using the technical content disclosed above to make slight changes or modifications are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A method for regenerating a silicon-aluminum molecular sieve, characterized in that: The deactivated silicon-alumina molecular sieve is dissolved in carbon deposits with supercritical carbon dioxide fluid, and then washed with acid to use the silicon and aluminum sources to synthesize the regenerated silicon-alumina molecular sieve.

2. The regeneration method according to claim 1, characterized in that The following steps are involved: a) Pretreatment placing the deactivated silica-alumina molecular sieve in an inert atmosphere and pretreating it at 120-300° C. for not less than 1 hour to obtain a pretreated sample; b) Supercritical carbon dioxide fluid treatment placing the pretreated sample in a supercritical fluid reaction device to perform supercritical carbon dioxide fluid treatment to obtain a supercritical carbon dioxide fluid-treated sample; c) Ultrasonic pickling placing the sample treated with supercritical carbon dioxide fluid in an acidic solution and performing acid washing in ultrasound to obtain an ultrasonically acid washed sample; b) synthesizing the regenerated silica-alumina molecular sieve The ultrasonically acid-washed sample is used as a silicon source and an aluminum source to synthesize the regenerated silica-alumina molecular sieve.

3. The regeneration method according to claim 1, characterized in that The conditions for the supercritical carbon dioxide fluid treatment in step b) are: temperature of 30-40° C., pressure of 7-9 MPa, and treatment time of 2-3 hours.

4. The regeneration method according to claim 1, characterized in that The step b) is: The pretreated sample is placed in a supercritical fluid reaction device, subjected to supercritical carbon dioxide fluid treatment, and then reduced to normal pressure to obtain a supercritical carbon dioxide fluid treated sample.

5. The regeneration method according to claim 4, characterized in that: The pressure reduction rate to normal pressure is 0.5-1 MPa / min.

6. The regeneration method according to claim 1, characterized in that The acidic solution in step c) is a dilute nitric acid solution with a mass fraction of 5 to 10%; The pickling time is 30-60 minutes.

7. The regeneration method according to claim 1, characterized in that: Step d) is: Alkali, an organic template and silica sol are added to the sample after ultrasonic acid washing, and then hydrothermal crystallization is performed to obtain the regenerated silica-alumina molecular sieve.

8. The regeneration method according to any one of claims 1 to 7, characterized in that: The silicon-aluminum molecular sieve is ZSM-5 molecular sieve.

9. A catalyst for producing aromatics by hydrogenation of CO2, characterized in that The catalyst is a composite catalyst composed of the regenerated ZSM-5 molecular sieve obtained by the regeneration method according to claim 8, which is dried and calcined, and an iron-based catalyst.

10. A method for preparing aromatics by hydrogenating CO2, characterized in that: Using the CO2 hydrogenation to aromatics catalyst according to claim 9; The reaction pressure is 2-3 MPa, the reaction temperature is 280-340° C., and the space velocity is 2000-20000 mL / (g·h).

Images